A key that turns fine when the door’s open but jams solid the second you pull it shut is one of the most common door problems there is, and also one of the easiest to misdiagnose. Nine times out of ten it isn’t the lock at all. It’s the door, sitting a millimetre or two out of true, so the locking points are trying to drive into keeps that no longer line up. The fix is usually a hinge adjustment, not a new mechanism, and it usually takes less time than reading the forum thread that sent you looking for an answer.
Key Takeaways
- A key that turns when the door is open but not when it’s closed almost always means the door has dropped or shifted, not that the lock is broken.
- Hinge adjustment with a 4mm or 5mm Allen key corrects the great majority of these cases.
- Keeps and grub screws are the second thing to check — loose or shifted keeps stop hooks and bolts engaging even on a well-aligned door.
- Adjustment fixes position. It cannot fix a worn gearbox, a cracked keep, or a door that’s actually warped.
- If the same door needs adjusting every few months, that’s a symptom worth listening to, not a maintenance routine.
- DIY adjustment on an installer-fitted door is generally fine, but check your paperwork before you start if the door is still under guarantee.
Why This Actually Happens
uPVC doors move. Not dramatically, but enough to matter. The panel expands and contracts with temperature, the frame settles slightly into its opening over the months after fitting, and the hinges — carrying the full weight of the door on a handful of screws — take a small amount of drop over time. None of this is a fault. It’s what happens to a heavy moving object hung in a frame, in every house.
The multipoint locking mechanism only works if the hooks, bolts and rollers along its edge land precisely inside their keeps when the door closes. Drop the door by two or three millimetres and those points no longer line up. The key still turns the cylinder fine — that part hasn’t changed — but the mechanism can’t drive the locking points home, so it binds or refuses to turn at all.
Quick Checks Before You Reach For The Allen Key
Close the door slowly and watch where it makes contact with the frame — if the top or bottom catches first, that tells you which way it’s dropped. Lift the handle slightly while turning the key; if the lock suddenly turns freely, the door has sagged and adjustment will very likely sort it. Look along the edge for scuff marks, a hook hitting the edge of a keep rather than sliding into it, or a grub screw that’s clearly missing.
Adjusting The Hinges And Keeps
Most uPVC doors use flag hinges with adjustment screws hidden under a cap on the hinge face, usually taking a 4mm or 5mm Allen key. Vertical adjustment (raising or lowering the door) is normally the top screw on each hinge; lateral adjustment, moving the door closer to or further from the seal, sits on a separate screw further down. Work in quarter turns and test the door after each small change rather than cranking the screw and hoping — over-adjusting is the most common mistake, and it tends to trade one problem for another.
If the hinges are square but the door still won’t lock cleanly, check the keeps themselves. They’re usually held with two small screws and can be repositioned slightly, or simply retightened if a grub screw has backed out over time. A slotted fixing hole gives a few millimetres of side-to-side movement — enough to bring a keep back in line with a hook or bolt landing just off target.
An Allen key set covering 3mm to 6mm, a cross-head screwdriver and a can of silicone-based lubricant will cover almost every case. Avoid oil-based sprays on the mechanism itself — silicone doesn’t attract grit the way oil does.
What Adjustment Can’t Fix
This is the part most online guides skip, and it’s the part that actually matters. Hinge and keep adjustment corrects position. It cannot correct wear. If you’ve adjusted the hinges and the door still won’t lock, or it locks today and needs adjusting again within a few weeks, the problem probably isn’t alignment any more. A worn gearbox inside the mechanism will bind and drag regardless of how well the door is hung. A cracked or distorted keep won’t hold a hook square no matter where you position it. A door that’s genuinely warped — twisted along its length rather than just dropped — will fight the frame at one point even when every other point lines up. None of these respond to an Allen key, and forcing the adjustment further usually just accelerates the wear on whatever’s actually failing.
This is also where the door’s history matters. How a door sits in its frame from day one depends heavily on how carefully it was hung and packed at installation, covered in more depth in why alignment and level matter in door installation. A door that was slightly out from the start tends to keep drifting back out no matter how often you correct it.
Warranty And When To Call A Fitter
Routine hinge and keep adjustment is unlikely to affect a guarantee on its own, but terms vary between installers, so it’s worth checking your own paperwork rather than assuming — see what guarantees you should expect from window and door installers for what a reasonable one actually includes.
If two or three careful adjustments haven’t solved it, or the problem keeps returning, stop and call someone rather than keep tightening screws. A fitter can quickly tell whether you’re looking at a worn mechanism, a cracked keep, or a door that’s reached the point covered in common front door problems and when to replace yours. A door that won’t lock properly is also a security issue, not just an inconvenience, so it’s worth checking the mechanism meets a reasonable standard, set out in our guide to door locks and PAS 24 standards. If it does turn out the door needs replacing, a proper survey is the only way to get an accurate picture of the frame and opening — see what happens during a door survey, or start by comparing what’s available on our uPVC doors page.
Frequently Asked Questions
Why won’t my key turn when the door is closed but works fine when it’s open?
This is the classic sign of a dropped or misaligned door. The cylinder itself is fine; the locking points simply aren’t lining up with their keeps when the door is shut, so the mechanism binds. Hinge adjustment usually resolves it.
Can I adjust a uPVC door lock myself?
Yes, in most cases. Hinge and keep adjustment is a standard homeowner-level job with an Allen key and a screwdriver. Work in small increments and test after each change.
How much does it cost to get a uPVC door professionally adjusted?
A straightforward adjustment callout sits toward the lower end of a general callout charge as a rough UK market range. A worn mechanism replacement costs more, and any fitter should give you a firm price after a look rather than over the phone.
Will adjusting the hinges myself void my door’s warranty?
Routine external adjustment is unlikely to on most doors, but terms vary by installer and product, so check your own paperwork rather than assume, especially before doing anything beyond the visible adjustment screws.
How often should uPVC doors need re-adjusting?
Occasionally, particularly after the first year while the frame settles and through seasonal temperature swings, is normal. Needing it every few weeks is not, and points to wear rather than routine movement.
What does it mean if the door still won’t lock after adjustment?
It usually means the fault has moved past simple alignment — a worn gearbox, a damaged keep, or a genuinely warped door are the common culprits, and none of these are fixed by further adjustment.
The Honest Answer
Most doors that won’t lock are suffering from position, not damage, and a careful hinge adjustment sorts them in minutes. The judgement call is knowing when to stop adjusting and start asking why the same fix keeps being needed — that’s the difference between routine maintenance and a door that’s quietly telling you it’s on its way out.